Zoom lens device with zooming position detector

ABSTRACT

A zoom lens device has a zooming position detector consisting of a code plate and a brush device. The code plate is mounted to a front face of a shutter unit that is attached to a front end of an axial movement barrel. The axial movement barrel is located inside a helical movement barrel so as to be immovable in the axial direction relative to the helical movement barrel, but is rotated relative to the helical movement barrel for zooming. The brush device is mounted to an inner peripheral portion of a lens barrel that is located near the face of the shutter unit and rotates relative to the face of the shutter unit, such that the electric contact strips brush the code plate while the shutter unit rotates relative to the lens barrel for zooming. A zooming position of the zoom lens device is determined based on output signals from the brush device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of copending application Ser. No.09/118,084, now U.S. Pat. No. 5,926,322, filed Jul. 17, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens device whose lens barrelelements rotate relative to each other for changing the focal length,i.e. for zooming. The present invention relates more particularly to azoom lens device having a zooming position detector mounted in a compactfashion.

2. Background Arts

A zoom lens device has at least front and rear lens groups whosepositions are changed relative to a film surface and relative to eachother in the direction of the optical axis of the zoom lens device.Since there is a clearance between barrels that hold the front and rearlens groups respectively, extraneous light would enter inside the zoomlens device through the clearance without any light-shielding device.JPY 5-31634 discloses a light-shielding device for a zoom lens device,which is constituted of a light-shielding ring having a resilient liparound its inner rim. The light-shielding ring is placed behind a faceflange surrounding an opening of a front wall of a camera body such thatthe resilient lip stays in contact with the outer periphery of a lensbarrel or lens cover frame that moves with the front lens group in theaxial direction through the opening of the front wall.

The light-shielding ring disclosed in JPY 5-31634 is useful for aclearance around a lens barrel that moves in the axial directionrelative to a fixed barrel. However, the light-shielding ring is notpreferable for a lens device where a front lens frame is rotatably heldin a barrel, and a front cover member having an opening for exposing thefront lens is attached to a front end of the barrel, and a clearance isprovided between the front lens frame and the front cover member forallowing the front lens frame to rotate relative to the front covermember. If the light-shielding ring is used for the clearance betweenthe front cover member and the front lens frame, the outer periphery ofthe front lens frame would rub against the lip of the light-shieldingring as the front lens frame rotates relative to the front cover member.The friction between the front lens frame and the front cover memberwould raise the necessary driving force for the lens device. The lip ofthe light-shielding ring would sooner be worn out or heat-deformed bythe frequent friction. Besides, the light-shielding ring increases therequisite number of parts necessary for the lens device.

On the other hand, it is known in the art to provide a zooming positiondetector in a zoom lens device. For example, JPA 50-36118 discloses azooming position detector consisting of an encoder plate and a brushdevice. The encoder plate is coupled to a lens barrel of a zoom lensdevice through gears and a lead screw, such that the encoder plate movesin the axial direction of the zoom lens device as the lens barrelrotates for zooming. As the encoder plate moves in the axial direction,the brush device brushes conductor patterns on the encoder platedetecting signals corresponding to the rotational angle of the lensbarrel. Japanese Utility Model Registration No. 2521469 discloses azooming position detector wherein a code plate having conductor patternsare tightly provided on an outer periphery of a cam ring that rotatesfor zooming, whereas a brush device brushing the conductor patterns issecured to a stationary frame outside the cam ring.

Either of the prior zooming position detectors needs a mounting spaceoutside the movable lens barrel, which inevitably enlarges the wholesize of the camera.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is toprovide a zoom lens device having a zooming position detector which doesnot need a specific space outside the zoom lens device.

Another object of the present invention is to provide a light-shieldingdevice for preventing extraneous light entering inside a lens devicethrough a clearance between a front cover member of the lens device anda member that is placed behind the front cover member and rotatesrelative to the front cover member.

To achieve the first object, a zoom lens device according to the presentinvention is comprised of a cylindrical lens barrel; a member that ismounted inside the lens barrel, the member being immovable in thedirection of an optical axis of the zoom lens device relative to thelens barrel, but rotating about the optical axis relative to the lensbarrel during zooming; a code plate mounted to one of a face of themember and an inner portion of the lens barrel that is located near theface of the member and rotates relative to the face of the member; abrush device having electric contact strips, the brush device beingmounted to the other of the face of the member and the inner portion ofthe lens barrel, such that the electric contact strips brush the codeplate while the member rotates relative to the lens barrel for zooming;and a determination device for determining a zooming position of thezoom lens device based on a rotational position of the lens barrelrelative to the member that is shown by output signals from the electriccontact strips.

According to a preferred embodiment, the member is a shutter unit intowhich a shutter mechanism and an actuator for the shutter mechanism areincorporated, and the lens barrel is a helical movement barrel thatmoves in the direction of the optical axis while rotating inside abarrel fixed to a camera body, whereas the shutter unit is secured to afront of an axial movement barrel that moves in the direction of theoptical axis together with the helical movement barrel without rotatingrelative to the fixed barrel.

As the code plate and the brush device are located inside the lensbarrel, they do not need any specific room outside the lens barrel ofthe zoom lens device.

To achieve the second object, a lens device according to the presentinvention is comprised of a lens barrel, an internal member that ismounted inside the lens barrel and rotatable about an optical axis ofthe zoom lens device relative to the lens barrel but immovable in adirection of the optical axis relative to the lens barrel, and a frontcover member secured to a front end of the lens barrel, the front covermember having an opening for exposing a center portion of the internalmember, wherein a front face of the internal member and a rear surfaceof the front cover member are engaged with each other through alabyrinth engagement, and a clearance is provided in between theinternal member and the front cover member for allowing the internalmember to rotate relative to the front cover member.

According to a preferred embodiment, the internal member is a front lensframe, and a circular groove is formed in one of the front face of thefront lens frame and the rear surface of the front cover member; and acircular ridge is formed in the other of the front face of the frontlens frame and the rear surface of the front cover member, the circularridge being fitted in the circular groove with the clearance.

Because of the labyrinthine engagement or the meanders of the clearance,extraneous light entering through the clearance is attenuated so muchthat it does not reach inside the lens device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention willbecome apparent from the following detailed description of the preferredembodiments when read in connection with the accompanying drawings,which are given by way of illustration only and thus are not limitativeof the present invention, wherein like reference numerals designate likeor corresponding parts throughout the several views, and wherein:

FIG. 1 is an exploded perspective view of a zoom lens device accordingto a first embodiment of the invention;

FIG. 2 is an axial sectional view of the zoom lens device of the firstembodiment at a wide-angle terminal;

FIG. 3 is a radial sectional view of the zoom lens device of the firstembodiment viewed from the film surface side;

FIG. 4 is an unfolded view of a cam barrel viewed from the outerperiphery;

FIG. 5 is an enlarged axial sectional view showing the front portion ofthe zoom lens device of the first embodiment;

FIG. 6 is an axial sectional view of the zoom lens device of the firstembodiment at a telephoto terminal;

FIG. 7 is a front view of a shutter unit of the zoom lens device, havinga zooming position detector and a front lens frame attached thereto;

FIG. 8 is an explanatory diagram of a code plate of the zooming positiondetector;

FIG. 9 is a front view of a shutter unit having a code plate accordingto a second embodiment;

FIG. 10 is an axial sectional view of essential parts of a zoom lensdevice according to a third embodiment of the present invention;

FIG. 11 is an exploded perspective view of a rear lens frame and anaxial movement barrel having synthetic fiber strips as a resilientdevice according to the third embodiment;

FIG. 12 is an enlarged view of a cam follower pin of the rear lens frameand a cam groove of a helical movement cam barrel of the thirdembodiment;

FIG. 13 is an axial sectional view of essential parts of a zoom lensdevice according to a fourth embodiment of the present invention;

FIG. 14 is an enlarged view of a cam follower pin of a rear lens frameand a polyester film ring as a resilient device according to the fourthembodiment; and

FIG. 15 is an explanatory diagram illustrating the operation of theresilient device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIGS. 1 and 2, a zoom lens device according to a firstembodiment is applied to a two component mechanical compensation typezoom lens system consisting of two lens groups. The zoom lens device ismainly constituted of a fixed barrel 10, a helical movement barrel 11, adrive ring 12, a front lens frame 13 holding a front lens group, a rearlens frame 14 holding a rear lens group, an axial movement barrel 15, acam barrel 16, a shutter unit 17, an axial movement guide ring 18 and adecorative cover plate 19.

The fixed barrel 10 has an internal or female helicoid 20 around itsinner periphery. The helical movement barrel 11 has an external or malehelicoid 21 around its outer periphery, which is engaged with theinternal helicoid 20 of the fixed barrel 10. Thereby the helicalmovement barrel 11 can rotate inside the fixed barrel 10 about anoptical axis 22 of the lens system while moving in the axial directionaccording to the lead of the helicoids 20 and 21. The decorative coverplate 19 is attached to the front end of the helical movement barrel 11.The front lens frame 13, the shutter unit 17, the cam barrel 16, theaxial movement barrel 15, the rear lens frame 14, the drive ring 12 andthe axial movement guide ring 18 are mounted in the helical movementbarrel 11 in this order from the front, wherein front is the objectiveside, and rear is the image side.

The shutter unit 17 and the axial movement guide ring 18 are secured tothe front and rear ends of the axial movement barrel 15 respectively.The axial movement barrel 15, the shutter unit 17 and the axial movementguide ring 18 are movable together with the helical movement barrel 11in the direction of the optical axis 22. The axial movement guide ring18 has three radial projections 23 formed at regular intervals aroundits outer circumference. The radial projections 23 are inserted in threeaxial slits 24 of the fixed barrel 10, so that the axial movement barrel15 and the shutter unit 17 cannot rotate inside the fixed barrel 10,while the helical movement barrel 11 is rotatable about the optical axis22 relative to the axial movement barrel 15. The front lens frame 13 issecured to the front end of the shutter unit 17.

A gear 25 is mounted to one of the radial projections 23 of the axialmovement guide ring 18. The gear 25 is in mesh with a drive gear 26through one of the axial slits 24 of the fixed barrel 10. The drive gear26 transmits the rotational movement of the motor 27 to the gear 25. Thedrive gear 26 has a length in its axial direction that is parallel tothe optical axis 22, so the gear 25 stays in engagement with the drivegear 26 while the helical movement barrel 11 is moving along the axialdirection.

The drive ring 12 is held between the rear end of the axial movementbarrel 15 and the axial movement guide ring 18 so as to be rotatableabout the optical axis 22. The drive ring 12 is formed with a gear 28through a limited angular range of the outer periphery. The drive ring12 also has three axial legs 30 spaced at regular intervals in thecircumferential or rotational direction thereof. The axial legs 30 areequal in size, and are fitted into three stepped recess portions 31 ofthe inner periphery of the helical movement barrel 11 which are arrangedin correspondence with the axial legs 30. The stepped recesses 31 have alength in the circumferential direction of the helical movement barrel11, that is greater than a circumferential length of the axial legs 30,so that the axial legs 30 are movable inside the stepped recesses 31 inthe circumferential direction through a given limited angle. The angleis given by a difference between the circumferential length of thestepped recess 31 and that of the axial leg 30. That is, the drive ring12 is coupled to the helical movement barrel 11 as to be rotatablerelative to the helical movement barrel 11 within the given angle. Acutout 29 is formed in the rear end of the helical movement barrel 11through a limited angular range in correspondence with the gear 28, forgiving the gear 25 access to the gear 28. In this way, the motor 27 canrotate the drive ring 12 through the gears 26, 25 and 28.

The cam barrel 16 is fitted onto the axial movement barrel 15 such thatthe cam barrel 16 is rotatable about the optical axis 22 and movablealong the optical axis 22 on the axial movement barrel 15. The cambarrel 16 has three axial guide ridges 32 on its outer periphery spacedat regular intervals in the circumferential direction. The axial guideridges 32 are engaged in three axial guide grooves 33 which arecorrespondingly formed the inner periphery of the helical movementbarrel 11. The axial guide grooves 33 are longer in the axial directionthan the axial guide ridges 32, but substantially equal in width to theaxial guide ridges 32. Thus the cam barrel 16 is movable along theoptical axis 22 relative to the helical movement barrel 11, but rotatestogether with the helical movement barrel 11.

The axial movement barrel 15 holds the rear lens frame 14 therein. Therear lens frame 14 has three cam follower pins 34 protruding radiallyoutwardly from a holder or frame of the rear lens frame 14. The camfollower pins 34 are spaced at regular intervals in the circumferentialdirection, and are engaged in three cam grooves 36 through three axialguide slits 35 of the axial movement barrel 15, so that the rotation ofthe cam barrel 16 causes the pins to move along the cam grooves 36. Thecam grooves 36 are helical about the optical axis 22 and are parallel toeach other. According to this configuration, when the helical movementbarrel 11 rotates, the rear lens frame 14 moves along the optical axis22 inside the axial movement barrel 15, that is, inside the helicalmovement barrel 11, while being stopped from rotating by the axial guideslits 35. In this way, the rear lens frame 14 moves in the axialdirection relative to the front lens frame 13, thereby varying thedistance to the front lens frame 13.

For zooming, the drive ring 12 is rotated by the motor 27 more than thegiven angle allowed for the relative rotation of the drive ring 12 tothe helical movement barrel 11. As shown in FIG. 3, when the drive ring12 rotates more than the given angle, one side edges 30a or 30b of theaxial legs 30 come into contact with one side walls 31a or 31b of thestepped recesses 31, so the rotation of the drive ring 12 is transmittedto the helical movement barrel 11, causing the helical movement barrel11 to rotate together. The rotation of the helical movement barrel 11causes the helical movement barrel 11 to move along the optical axis 22in accordance with the lead of the helicoids 20 and 21. The front lensframe 13 is moved in the axial direction together with the helicalmovement barrel 11, and the cam barrel 16 is rotated together with thehelical movement barrel 11. The rotation of the cam barrel 16 causes therear lens frame 14 to move in the axial direction relative to thehelical movement barrel 11 because of the engagement of the cam followerpins 34 in the cam grooves 36 through the axial guide slits 35. In thisway, the axial positions of the rear lens frame 14 and the front lensframe 13 are changed to vary the focal length of the zoom lens in acontinuous fashion.

As the axial legs 30 moves within the stepped recesses 31, the frontlens frame 13 rotates relative to the decorative cover plate 19. Asshown in detail in FIG. 5, the front lens frame 13 has a circular groove13a formed in its front face, for accepting a circular ridge 19a that isformed on the inside or rear surface of the decorative cover plate 19. Aclearance S is provided between the front lens frame 13 and thedecorative cover plate 19, such that the front lens frame 13 can rotaterelative to the decorative cover plate 19 without any friction.Therefore, the wearing of these members 13 and 19 is little, and thedriving power necessary for this relative rotation is small. Because ofthe labyrinthine engagement between the front lens frame 13 and thedecorative plate 19, extraneous light falling into the clearance S isattenuated at the meanders of the clearance S, and does not reach insidethe helical movement barrel 11.

Cam projections 40 are formed integrally on the inside surfaces of therespective axial legs 30. The cam projections 40 are engaged in threefocusing cam grooves 41 which are formed around the outer periphery ofthe cam barrel 16 at regular intervals. As shown in detail in FIG. 4,the focusing cam grooves 41 are also helical about the optical axis 22but have different courses from those of the cam grooves 36. Forfocusing, the drive ring 12 is rotated relative to the helical movementbarrel 11, that is, within the given angle determined by the movablerange of the axial legs 30 within the stepped recesses 31. With therelative rotation of the drive ring 12 to the helical movement barrel11, the cam projections 40 moves along the focusing cam grooves 41.

Indeed the cam projections 40 apply forces to the cam grooves 41 both inthe circumferential direction and in the axial direction, but the forcenecessary for rotating the helical movement barrel 11 is so large thatthe helical movement barrel 11 is not moved by the force applied fromthe cam projections 40 in the circumferential direction to the camgrooves 41. The cam barrel 16 is hindered from rotating relative to thehelical movement barrel 11 because of the engagement between the axialguide ridges 32 of the cam barrel 16 and the axial guide grooves 33 ofthe helical movement barrel 11. Therefore, so long as the axial legs 30move within the stepped recesses 31 and thus the driving force isapplied only from the cam projections 40 to the cam grooves 41, thehelical movement barrel 11 does not rotate and move, and thus the focallength is maintained unchanged. Only the cam barrel 16 is moved in theaxial direction. With the axial movement of the cam barrel 16, the camgrooves 36 push the cam follower pins 34 in the axial direction, so thatthe rear lens frame 14 moves in the axial direction. In this way, onlythe rear lens frame 14 is moved for focusing.

As shown in FIG. 6, the motor 27 is driven by a controller 46 through adriver 45. There is a reduction gear train 47 from a drive shaft gear27a of the motor 27 to the drive gear 26. The controller 46 controlszooming by driving the motor 27 in response to a zooming switch providedin a console 48. The zooming switch includes a telephoto zooming buttonfor changing the focal length to the telephoto side, and a wide-anglezooming button for changing the focal length to the wide-angle side. InFIGS. 2 and 6, designated by 49 and 50 are a film surface and a frontwall of the camera body respectively.

The controller 46 controls zooming, and then sets the lens device to oneof predetermined initial focusing positions as set forth in detailbelow. Thereafter, responsive to a halfway depression of a shutterbutton, the controller 46 controls focusing. When the shutter button ispressed farther to the full, the controller 46 activates a shuttermechanism to make an exposure. Thereafter, the controller 46 resets thelens device to the initial focusing position, preparing for the nextshutter button operation. The controller 46 performs these operationsaccording to a sequence program stored in a ROM 51.

An encoder wheel 52 having radial slits is mounted on the drive shaft ofthe motor 27, so as to rotate together with the drive shaft. A photosensor 53 is disposed in the course of the encoder wheel 52, to detectthe slits of the encoder wheel 52 and output an encoder pulse signal tothe controller 46. The controller 46 determines rotational angle of themotor 27 based on the encoder pulse signal. The controller 46 controlsstart and stop of the motor 27 with reference to the rotational angleduring the setting to the initial focusing position and the focusing.

As described so far, according to the configuration of the presentinvention, it is possible to vary the focal length continuously.However, as the focusing is made by moving the rear lens frame 14 in thedirection of the optical axis 22 while maintaining the zooming positionunchanged, the amount of movement of the rear lens frame 14 necessaryfor focusing on the same subject range varies depending upon the zoomingposition. Therefore, it is preferable to predetermine a plurality ofzooming positions at appropriate intervals so as to simplify thefocusing control.

As shown in detail in FIG. 7, the shutter unit 17 has a shuttermechanism and an actuator 57 for driving the shutter mechanism areincorporated therein. On the front face of the shutter unit 17, there isa semicircular code plate 55. A brush device 56 is secured to an innerfront portion of the helical movement barrel 11, such that the brushdevice 56 slides on or brushes the code plate 55 with the rotation ofthe helical movement barrel 11. The code plate 55 and the brush device56 constitute a zooming position detector. As the zooming positiondetector is located in a room between the shutter unit 17 and thedecorative cover plate 19, it is unnecessary to provide a specificmounting space for the zooming position detector by enlarging thediameter of the lens device or the whole scale of the camera. The codeplate 55 is easy attachable to the shutter unit 17 by use of a simpledevice such as bolts or heat caulking. In the shown embodiment, the codeplate 55 has holes 55a and 55b at its opposite sides, and caulkingbosses 17a are integrally formed with a plastic base plate of theshutter unit 17. By heat-deforming the caulking bosses 17a in the holes55a and 55b, the code plate 55 is attached to the shutter unit 17.

The brush device 56 has a pair of signal brushes 56a and 56b and anearth brush 56c. The code plate 55 consists of three signal contactpatterns Ea, Eb and Ec, and an earth contact pattern GRD. As the helicalmovement barrel 11 rotates, the signal brush 56a brushes the signalcontact patterns Ea and Eb, and the signal brush 56b brushes the signalcontact pattern 56c, whereas the earth brush 56c brushes the earthcontact pattern GRD.

In FIG. 8, contact positions Z1, Z2, Z3, Z4 and Z5 of the brush device56 on the code plate 55 correspond to the predetermined zoomingpositions, wherein the contact position Z1 corresponds to the wide-angleterminal as shown in FIG. 2, the contact position Z5 corresponds to the5 telephoto terminal as shown in FIG. 6, and the contact positions Z2,Z3 and Z4 correspond to three zooming positions between the terminals.When the helical movement barrel 11 rotates to the wide-angle terminalZ1, the signal brush 56a comes into contact with a portion Eb1 of thecontact pattern Eb, whereas the signal brush 56b comes into contact witha portion Ec1 of the contact pattern Ec. When the helical movementbarrel 11 rotates to the zooming position Z2, the signal brush 56a comesinto contact with a portion Ea1 of the contact pattern Ea. When thehelical movement barrel 11 rotates to the zooming position Z3, thesignal brush 56a comes into contact with a portion Eb2 of the contactpattern Eb. When the helical movement barrel 11 rotates to the zoomingposition Z4, the signal brush 56b comes into contact with a portion Ec2of the contact pattern Ec. When the helical movement barrel 11 rotatesto the telephoto terminal Z5, the signal brush 56a comes into contactwith a portion Ea2 of the contact pattern Ea, whereas the signal brush56b comes into contact with a portion Ec3 of the contact pattern Ec.

The controller 46 identifies the present zooming position by signalsfrom the signal brushes 56a and 56b. In this instance, the signals fromthe signal brushes 56a and 56b represent "011" for the wide-angleterminal Z1, "100" for the zooming position Z2, "010" for the zoomingposition Z3, "001" for the zooming position Z4, and "101" for thetelephoto terminal Z5.

The controller 46 controls zooming by driving the motor 27 to rotate inforward or reverse direction depending upon whether the telephotozooming button or the wide-angle zooming button is operated. When theoperation on the zooming button is terminated, the controller 46decelerates the motor 27. Thereafter when the signal brushe 56a or 56boutputs a signal, the controller 46 stops the motor 27. Thus, after thezooming, the zoom lens device always stops at one of the predeterminedzooming positions Z1 to Z5 where at least one of the signal brushes 56aand 56b is in contact with any of the contact patterns Ea to Ec.

In order to detect the focusing position with accuracy, it is desirableto detect the position of the cam barrel 16 in the axial direction by aspecific position detector. In order to cut the cost, however, theabove-described zooming position detector may double as an initialfocusing position detector. Specifically, the helical movement barrel 11is rotated a little from the present zooming position to the telephotoside till the cam projections 40 move to one terminals of the camgrooves 41. In this position, the cam barrel 16 moves to a rearmostposition or the nearest position to the film surface 49 in its axialmovement range. In result, the signal brush 56a or 56b moves from thezooming position to one of the initial focusing positions P1, P2, P3, P4and P5 that are located on the telephoto side of the respective zoomingpositions.

For focusing, the controller 46 drives a range finding section 59 toobtain a subject distance, and determines a pulse number correspondingto the subject distance with reference to the ROM 51. Thereafter, thecontroller 46 rotates the motor 27 in the forward direction to rotatethe helical movement barrel 11 to the telephoto side. As soon as thesignal brushes 56a and 56b are put out of the signal contact pattern Eato Ec, the controller 46 decelerates the motor 27 and starts countingpulses from the photo sensor 53. The controller 46 first counts down thephoto sensor pulses from a constant pulse number that is stored in theROM 51 and is given for setting the lens device from any of the zoomingpositions Z1 to Z5 to the nearest one of the initial focusing position.Accordingly, when the count comes down to zero, the controller 46 startscounting up the pulses from the photo sensor 53, and compares the countto the pulse number corresponding to the subject distance. When thecount reaches the pulse number determined by the subject distance, thecontroller 46 stops the motor 27. The drive ring 12 rotates within thegiven angle for focusing, so that the helical movement barrel 11 doesnot rotate during the focusing.

Since the amount of axial movement of the rear lens group 14 necessaryfor focusing varies even on the same subject distance depending upon thezooming position, the ROM 51 stores different pulse numbers to the samesubject distance for the respective zooming positions. When a shutterrelease operation has been made after the focusing, the controller 46drives the motor 27 to rotate in the reverse direction to rotate thehelical movement barrel 11 to the wide-angle side till the signal brush56a or 56b gets back to the preceding zooming position. Then thecontroller 46 stops the motor 27 for a moment, and makes the samecontrol as above to set the signal brush 56a or 56b to one of theinitial focusing positions P1 to P5 nearest to the preceding zoomingposition. In this way, the zoom lens device is positioned at one of theinitial focusing positions P1 to P5 without the need for any specificposition detector separately from the zooming position detector thatconsists of the code plate 55 and the brush device 56.

As described above, the cam follower pins 34 of the rear lens frame 14are engaged in the axial guide slits 35 of the axial movement barrel 15and the cam grooves 36 of the cam barrel 16, such that the rear lensframe 14 moves along with the movement of cross points between the camgrooves 36 and the axial guide slits 35 that is caused by the rotationof the cam barrel 16 with the helical movement barrel 11.

Now the operation of the zoom lens device having the above describedconstruction will be described.

The driving power of the motor 27 is transmitted to the gear 25 throughthe drive shaft gear 27a, the reduction gear train 47 and the drive gear26. The rotational movement of the gear 25 is transmitted to the drivering 12. When the front lens frame 13 and the rear lens frame 14 are inthe wide-angle terminal as shown in FIG. 2 where the zoom lens device isfully retracted, the signal brushes 56a and 56b are set at the initialfocusing position P1 nearest to the contact pattern portions Eb1 andEc1. In any of the initial focusing positions P1 to P5, one side edges30a of the axial legs 30 are in contact with the side walls 31a of thestepped recesses 31, whereas the cam projections 40 are located at theirnearest positions to closed ends of the cam grooves 41, where the cambarrel 16 is in its rearmost position of its axial movement range.

Responsive to a halfway depression of the shutter button at thewide-angle terminal, the controller 46 drives the range finding section59 to measure a subject distance, and reads out a pulse numbercorresponding to the subject distance and the constant pulse number forthe initial focusing position setting the ROM 51. Thereafter, thecontroller 46 drives the motor 27 in the reverse direction whilecounting down the pulses of the photo sensor 53 from the constant pulsenumber. When the count comes down to zero, the controller 46 startscounting up the pulses of the photo sensor 53. When the count comes upto the pulse number corresponding to the subject distance, thecontroller 46 stops the motor 27.

Although the reverse direction of the motor 27 is the direction torotate the helical movement barrel 11 to the wide-angle side, thehelical movement barrel 11 does not rotate during focusing because therotation of the motor 27 in the reverse direction is within the limitedangular range for focusing. Merely the drive ring 12 and thus the camprojections 40 rotates to the wide-angle side. Since the axial guideridges 32 of the cam barrel 16 are engaged in the axial guide grooves 33of the helical movement barrel 11, the cam projections 40 move insidethe cam grooves 41 while pushing front walls 41a of the cam grooves 41in the direction of the optical axis 22, thereby causing the cam barrel16 to move forward along the optical axis 22. When the controller 46stops the motor 27 upon counting up to the pulse number corresponding tothe subject distance, the cam projections 40 move to a focusing positioninside the cam groove 41 that is determined by the subject distance. Themovement of the cam barrel 16 caused by the movement of the camprojections 40 is transmitted to the cam follower pins 34 through thecooperation between the cam grooves 36 and the axial guide slits 35, sothat the rear lens frame 14 moves axially along with the cam barrel 16.In this embodiment, the focusing is performed by shifting the focus froma nearest range to an infinity range.

When the photographer further press the shutter button to the full, thecontroller 46 activates the shutter mechanism. After the exposure, thecontroller 46 resets the zoom lens device to the preceding initialfocusing position. First the controller 46 drives the motor 27 in thereverse direction. Since the reverse rotational direction of the motor27 is the direction to rotate the helical movement barrel 11 to thewide-angle side, the other side edges 30b of the axial legs 30 arebrought into contact with the other side walls 31b of the steppedrecesses 31. Further rotation of the motor 27 in the reverse directionis transmitted to the helical movement barrel 11 through the drive ring12, rotating the helical movement barrel 11 to the wide-angle side.

The controller 46 rotates the motor 27 in the reverse direction till thesignal brushes 56a and 56b come into contact with the contact patternportions Eb1 and Ec1. Then the controller 46 rotates the motor 27 in theforward direction till the signal brushes 56a and 56b are put off thecontact patterns Eb and Ec. That is, the drive ring 12 is rotated beyondthe given angle, bringing the side edges 30a of the axial legs 30 intocontact with the side walls 31a of the stepped recesses 31, and rotatingthe helical movement barrel 11 to the telephoto side. When the signalbrushes 56a and 56b leave the contact patterns Eb and Ec, the controller46 decelerates the motor 27, and starts counting the pulses from thephoto sensor 53. When the count reaches the pulse number for initialfocusing position, the controller 46 stops the motor 27. In this way,the signal brushes 56a and 56b are placed at the initial focusingposition P1, while the side edges 30a of the axial legs 30 are incontact with the side walls 31a of the stepped recesses 31, and the camprojections 40 are placed at the nearest position to the closed ends ofthe focusing cam grooves 41. Therefore, the cam barrel 16 is shifted toits rearmost position relative to the axial movement barrel 15.

When zooming to the telephoto side, the motor 27 is rotated in theforward direction so much that the drive ring 12 is rotated beyond thegiven angle, pushing the side walls 31a of the stepped recesses 31 ofthe helical movement barrel 11 by the side edges 30a of the axial legs30. The rotation of the helical movement barrel 11 in this directioncauses the helical movement barrel 11 to move forward in the directionof the optical axis 22 according to the lead of the helicoids 20 and 21.Along with the axial movement of the helical movement barrel 11, thefront lens frame 13, the rearmost lens frame 14 and the axial movementbarrel 15 moves in the axial direction.

The cam barrel 16 also rotates together with the helical movement barrel11 because the axial guide grooves 33 and the axial guide ridges 32.Since the cam projections 40 are located at the nearest positions to theclosed ends of the focusing cam grooves 41, the cam barrel 16 rotates inits rear position relative to the axial movement barrel 15. When the cambarrel 16 is rotated by the forward rotation of the motor 27, the rearlens frame 14 moves forward inside the helical movement barrel 11 whilebeing prevented from rotating by the cooperation between the axial guideslits 35 and the cam grooves 36. Thereby, the distance from the rearlens frame 14 to the front lens frame 13 is reduced.

After the zooming to the telephoto side is complete, the motor 27 isstopped when the signal brushe 56a or 56b comes into contact with thenext pattern portion, e.g. Ea1, in the zooming direction to thetelephoto side that corresponds to the forward rotation of the motor 27.The side edges 30a of the axial legs 30 stay in contact with the sidewalls 31a of the stepped recesses 31 during the zooming to the telephotoside. Thereafter, the controller 46 rotates the motor 27 further in theforward direction for setting the zoom lens device to the initialfocusing position till counting up to the constant pulse number afterthe signal brushes 56a and 56b are put off the contact patterns Ea andEb.

When zooming to the wide-angle side, the motor 27 is rotated in thereverse direction so much that the drive ring 12 is rotated beyond thegiven angle, pushing the side walls 31b of the stepped recesses 31 ofthe helical movement barrel 11 by the side edges 30b of the axial legs30. The rotation of the helical movement barrel 11 in this directioncauses the helical movement barrel 11 to move rearward. Since the camprojections 40 are located at nearest positions to open ends of thefocusing cam grooves 41 during the zooming to the wide-angle side, thecam barrel 16 rotates together with the helical movement barrel 11 inits foremost position relative to the axial movement barrel 15. When thecam barrel 16 is rotated by the reverse rotation of the motor 27, therear lens frame 14 moves rearward inside the helical movement barrel 11,so that the distance from the rear lens frame 14 to the front lens frame13 increases.

After the zooming to the wide-angle side is complete, the motor 27 isstopped when the signal brushe 56a or 56b comes into contact with thenext pattern portion in the zooming direction to the wide-angle sidethat corresponds to the reverse rotation of the motor 27. The side edges30b of the axial legs 30 stay in contact with the side walls 31b of thestepped recesses 31 during the zooming to the wide-angle side.Therefore, the controller 46 rotates the motor 27 in the forwarddirection to rotate the drive ring 12 beyond the limited angle, forsetting the zoom lens device to the initial focusing position after thezooming to the wide-angle side. Thereby, the side edges 30a are broughtinto contact with the side walls 31a. Thereafter, the helical movementbarrel 11 is rotated to the telephoto side till the pulses from thephoto sensor 53 is counted up to the constant pulse number from the timewhen the signal brushes 56a and 56b are put off the contact patterns Eaand Eb. In this way, regardless of the zooming direction and the zoomingposition, the cam projections 40 are set to the nearest positions to theclosed ends of the focusing cam grooves 41. That is, the cam barrel 16is always set in the same axial position relative to the helicalmovement barrel 11 at the start of focusing.

The code plate 55 having the code patterns 56a, 56b and 56c may bereplaced by a code plate 72 as shown in FIG. 9. The code plate 72 has anearth pattern 70 and a resistor pattern 71. The resistor pattern 71consists of a conductor layer 71a that extend along a semi-circularcourse of a signal brush 75a of a brush device 75 and a resistor layer71b that is provided on the conductor layer 71a as shown by hatching.The resistance of the resistor pattern 71 increases with the distancefrom an electrode 73. Accordingly, the potential difference between theresistor pattern 71 and the earth pattern 70, i.e. the voltage of theoutput signal from the brush device 75 increases as the signal brush 75aremoves from the electrode 73, that is, as the lens device is zoomed tothe telephoto side.

In the above embodiment, the code plate 55 is mounted to the shutterunit 17, and the brush device is mounted to the helical movement barrel11. However, it is possible to mount a code plate to the inner peripheryof the helical movement barrel, and a brush device to the shutter unit17. It is also possible to mount a brush device to the shutter unit 17,and a code plate to a rear side of a decorative cover plate that issecured to the front of a helical movement barrel. In other words,accordidng to the present invention, the brush device and the code plateof the zooming position detector of the present invention may berespectively mounted to those two parts of the lens barrel which areadjacent to each other and rotate relative to each other for zooming.

Although the first embodiment has been described with respect to a twocomponent mechanical compensation type zoom lens device consisting oftwo lens groups, the first embodiment is applicable to other types oflens device. Also the light-shielding device of the invention isapplicable to other types of lens device for preventing extraneous lightfrom entering through a clearance between a front cover member of thelens device, e.g. a decorative cover plate, and a member, e.g. a frontlens frame, that is placed behind the front cover member and rotatesrelative to the front cover member. The shape of labyrinth of theclearance between the decorative cover plate and the front lens frame isnot limited to that shown in the drawings. Instead of the circulargroove 13a and the circular ridge 19a, it is possible to form a circulargroove in the rear surface of a decorative cover plate and a circularridge on the front side of a front lens frame.

Meanwhile, where a front lens frame or a rear lens frames is engagedwith a lens barrel or the like through a helicoid engagement or anengagement between cam grooves and cam follower pins, a play orclearance is provided in the engaged portions for allowing relativemovement of the lens frame to the barrel. Without any measure, the playcauses fluctuation or inclination of the lens frame in the direction ofan optical axis of the lens system. To avoid such trouble, it is knownin the art to throw a coil spring across the front and rear lens framesso the helicoid or the cam follower pin of the lens frame is kept incontact with the same side of the helicoid or the cam groove.

However, because there are many restrictions on the coil spring, such asclosed height, deflection and required load, the design of the lensdevice, including the distance between the front and rear lens frames,is also restricted.

Moreover, where the minimum distance between the front and rear lensframes differs for much from the maximum distance, the resilience of thecoil spring increases at the minimum use length should be large enough.As a result, the load of the coil spring and thus the rotational torqueof the lens barrel vary so much that where the lens barrel is moved byan electromagnetic motor the zooming speed becomes unstable. Since thepower of the motor is determined by the largest possible rotationaltorque of the lens barrel, the power is wasted in other variation rangeof the rotational torque. It is possible to reduce the load of the coilspring at the minimum use length by reducing the spring constant of thecoil spring. But the spring constant can only be reduced by reducing thewire diameter of the coil spring or by elongating the free length orheight of the coil spring. Accordingly, reducing the spring constantmakes it difficult to assemble the coil spring in the lens barrel.

FIG. 10 shows essential parts of a zoom lens barrel 100 according toanother embodiment of the invention, that solves the above problem dueto the play in the engagement between the lens frame and the lensbarrel. An outermost barrel 112 is fixed at its rear end to a not-showncamera body. The fixed barrel 112 has a female helicoid 112a around itsinner periphery. A helical movement cam barrel 114 has a male helicoid114a around its outer periphery near the rear end, which is engaged withthe helicoid 112a. The helical movement cam barrel 114 is driven by anot-shown motor to move in the direction of an optical axis L whilerotating about the optical axis. Designated by 121 is a front coverplate.

The helical movement cam barrel 114 holds an axial movement barrel 116therein, such that the axial movement barrel 116 is rotatable relativeto the helical movement cam barrel 114 and movable in the axialdirection together with the helical movement cam barrel 114. Asubstantially cylindrical front lens frame 120 holding a front lensgroup 122 is fitted in between the axial movement barrel 116 and thehelical movement cam barrel 114 so as to be movable relative to thebarrels 116 and 114. The front lens frame 120 has a male helicoid 120aaround its outer periphery near the rear end, which is engaged in afemale helicoid 114c that is formed around the inner periphery of thehelical movement cam barrel 114 near the front end. The axial movementbarrel 116 stops the front lens frame 120 from rotating, so that thefront lens frame 120 moves in the axial direction while the helicalmovement cam barrel 114 rotates.

A rear lens frame 124 holding a rear lens group 126 has three radial camfollower pins 128 arranged around its outer periphery at intervals of120 degrees, as shown in detail in FIG. 11. Correspondingly, the axialmovement barrel 116 has three axial slits 116a that extend in parallelto the optical axis L. Through the axial guide slits 116a of the axialmovement barrel 116, the cam follower pins 128 are engaged in threeaxial cam grooves 114b formed in the inner periphery of the helicalmovement cam barrel 114, as shown in detail in FIG. 12.

A strip of resilient synthetic fiber 130 is cemented to the innerperiphery of the axial movement barrel 116 in parallel to each axialslit 116a, such that the rear lens frame 124 contacts the syntheticfiber strips.130 at its three outer peripheral zones 124a shown byhatching. While the front lens frame 120 moves in the axial directionalong with the rotation of the helical movement cam barrel 114, the rearlens frame 124 moves in the axial direction as the cam follower pins 128being guided along the axial slits 116a of the axial movement barrel116. Because of the friction between the rear lens frame 124 and thesynthetic fiber strips 130, the cam follower pins 128 are leaned on oneside walls of the cam grooves 114b of the helical movement cam barrel114. Thereby, the cam follower pins 128 stably slide along the axialslits 116a. Zooming is performed by changing the distance between thefront lens frame 120 and the rear lens frame 124 in this way.

To zoom the zoom lens barrel 100 to the wide-angle side, the rear lensframe 124 is moved rearward, i.e. away from the front lens frame 120. Atthat time, because of the friction between the outer periphery of therear lens frame 124 and the synthetic fiber strips 130, a power againstthe movement of the rear lens frame 124 is applied to the rear lensframe 124. Since the rear lens frame 124 moves rearward, i.e. to theright side in FIG. 10, the cam follower pins 128 lean on the front wallsof the cam grooves 114b, i.e. the left side wall of the cam grooves 114bin FIGS. 10 and 12.

To zoom the zoom lens barrel 100 to the telephoto side, the rear lensframe 124 is moved forward, i.e. toward the front lens frame 120. Alsoin this direction, the friction between the outer periphery of the rearlens frame 124 and the synthetic fiber strips 130 applies a poweragainst the movement of the rear lens frame 124 to the rear lens frame124, so that the cam follower pins 128 lean on the rear walls of the camgrooves 114b.

Accordingly, the rear lens frame 124 moves along with the helicalmovement cam barrel 114 without fluctuation or inclination, so that itis possible to control the distance between the front lens group 122 andthe rear lens group 126 with accuracy. Moreover, because the frictionalpower between the rear lens frame 124 and the helical movement cambarrel 114 is maintained unchanged in both zooming directions, the loadon the zoom lens barrel 100 is maintained unchanged. Therefore thetorque for moving the lens barrel 100 may always be constant, and thusthe workability of the zoom lens barrel 100 is improved.

As the synthetic fiber strips 130 are provided in a clearance betweenthe outer periphery of the rear lens frame 124 and the inner peripheryof the axial movement barrel 116, the synthetic fiber strips 130 do notneed any specific space and are preferable in terms of compactness. Thesynthetic fiber strips 130 may be replaced by any resilient members suchas polyester films that give an appropriate frictional resistanceagainst the movement of the rear lens frame 124. It is alternativelypossible to put resilient members on the cam follower pins 128 such thatthe resilient members are kept in contact with the inner periphery ofthe axial movement barrel 116.

FIG. 13 shows an embodiment where a polyester film 132 is mounted to arespective cam follower pin 128 of a rear lens frame 124. As shown inFIG. 14, the polyester film 132 is bent into a ring, and has holes 132aformed therethrough so the ring of polyester film 132 is fitted on thecam follower pin 128. Thereby, the polyester film rings 132 as resilientdevices are placed in between the rear lens frame 124 and an axialmovement barrel 116, as shown detail in FIG. 15. Because the polyesterfilm rings 132 apply a resistance or friction against the movement ofthe rear lens frame 124 relative to the axial movement barrel 16, thecam follower pins 128 lean on one side walls of cam grooves 114b of ahelical movement cam barrel 114 in the same way as shown in FIG. 12.Accordingly, the embodiment of FIG. 13 provide the same effect as theembodiment of FIG. 10.

It is possible to provide a resilient device like the synthetic fiberstrip 130 or the polyester film ring 132 on each cam follower pin of afront lens frame in case where the front lens frame is moved through acam mechanism.

Although the present invention has been described with respect to a zoomlens device, the present invention is applicable to a compact camera, avideo camera and any other types of cameras.

Thus the present invention should not be limited to the aboveembodiments but, on the contrary, various modifications of the presentinvention may be possible to those skilled in the art without departingfrom the scope of claims attached hereto.

What is claimed is:
 1. A lens device comprising a lens barrel, aninternal member that is mounted inside the lens barrel and rotatableabout an optical axis of the zoom lens device relative to the lensbarrel but immovable in a direction of the optical axis relative to thelens barrel, and a front cover member secured to a front end of the lensbarrel, the front cover member having an opening for exposing a centerportion of the internal member, wherein a front face of the internalmember and a rear surface of the front cover member are engaged witheach other through a labyrinthine engagement and a clearance is providedin between the internal member and the front cover member for allowingthe internal member to rotate relative to the front cover member;whereinone of the front face of the internal member and the rear surface of thefront cover member comprises a circular groove; and another of the frontface of the internal member and the rear surface of the front covermember comprises a circular ridge, the circular ridge being fitted inthe circular groove with the clearance.
 2. A lens device as claimed inclaim 1, wherein the internal member is a front lens frame holding alens in the center portion thereof.